20240613; version 4.046:
  * Code size reduction. SRELL no longer gives priority to finding a
    literal sequence.
  * Various minor improvements and fixes.

20240608; version 4.045:
  * Implemented the regex modifiers feature. But until the proposal is
    merged into the draft specification of ECMAScript, this feature is
    disabled and available only when SRELL_ENABLE_MODIFIERS is defined.
  * Added a missing check to see whether a backreference number exceeds
    the max number of capturing groups or not, which should have been
    added with the modification for the duplicate named capturing groups
    support in version 4.043.

20240602; version 4.044:
  * Added several missing #if ~ #endif directives for
    SRELL_NO_NAMEDCAPTURE.
  * Retired an older state insertion function in favour of a newer one.

20240526; version 4.043:
  * Implemented the duplicate named capturing groups feature.

20240524; version 4.042:
  * Expanded the scope of the optimisation for * and + also to support
    C{n,} where C is a character or character class and n >= 2.
  * Introduced the unified stack, which is used when either of the
    following conditions is met:
    1) The iterator passed to an algorithm function is a pointer, or
    2) std::is_trivially_copyable is supported by the compiler and for
       the type I of the passed iterator,
       std::is_trivially_copyable<I>::value is true.
    Otherwise separate stacks that have been present from early versions
    are used.

20240519; version 4.041:
  * Completed the temporary fix in 4.040.
  * Removed unused functions.
  * Fixed a potential issue on systems where memory of more than 64GB
    can be allocated.

20240131; version 4.040:
  * Restored one more line for ?? (non-greedy {0,1}) not to cause an
    optimisation bug.

20240127; version 4.039:
  * Restored some code that had been removed mistakenly in 4.037.

20240124; version 4.038:
  * Fixed a bug that caused /(?:ab)+|cd/ to match "ababcd".
    Condition: Both sides of | begin with different characters, and the
    left side character is contained in (?:)+.
  * Minor improvements.

20240122; version 4.037:
  * Fixed an optimisation bug that caused /(?:a|ab|abc)$/ to match "ac"
    since version 4.021.
    Condition: (?:A|B|C) where A is a prefix of B, and B is a prefix of
    C.
    -> A path from the end of A to a suffix of C occured through the
       wrong optimisation. This path was usually hidden, but could be
       used when backtracking is performed.
  * Other various improvements and fixes.

20240114; version 4.036:
  * Improvement and bugfix of lookaround (lookahead and lookbehind):
    1. Removed unnecessary stack operations.
    2. Restored the state type that had been removed in version 3.003 so
       that the value of the first capturing group in /(?:(?=(\w))|b)c$/
       against "abc" will be undefined, not "b".
       Condition: 1. A lookaround assertion contains a capturing group,
       2. After the lookaround assertion is successful, matching with
       succeeding expressions fails, 3, Another subpattern separated by
       '|' is tried and a match with total expressions is found.
       -> A subsequence captured by the group in the lookaround remained
          without being reverted to "undefined".
  * Replaced misc/sample01.cpp with conftest.cpp.
  * Tagged each kind of epsilon.

20231229; version 4.035:
  * Improved case folding of character classes. (Compilation of \p{Any}
    was a bit slow when the icase flag was set).
  * Several preparations for (?i:) support.
  * Updated updataout3.cpp. It could not be compiled because an internal
    namespace was changed in the previous version.

20231209; version 4.034:
  * Modified to use std::contiguous_iterator when it is available, to
    check if the iterator passed to an algorithm function is a
    contigous_iterator.
  * Modified match_results::operator[]() not to throw error_backref when
    a group name not existing in the regular expression is passed to as
    an argument, but to return a reference to a sub_match object
    representing an unmatched sub-exression.
    In accordance with this change, now
    match_results::operator[](size_type n) also returns the same object
    when n >= size(). (Behaviour accordant to std::regex. Until the
    previous version, this object was returned only when
    SRELL_STRICT_IMPL is defined).
  * Implemented the no throw/exception mode.
  * For the no throw mode, added basic_regex::ecode() that returns
    error_type that should have been thrown during the previous pattern
    compilation.
  * For the no throw mode, added match_results::ecode() that returns
    error_type that should have been thrown during the previous pattern
    matching/searching.

20230926; version 4.033:
  * Fixed a bug that could cause a crash on 64-bit systems since version
    4.020 (Thanks to Yuriy Skvortsov for the bug report).
    Condition: 3 or more Alternatives begin with the same character such
    as /ab|ac|ad/.
  * Removed an unused member function from utf_traits.
  * Some clean-ups.

20230916; version 4.032:
  * Added directives for decoders of UTF-8/UTF-16 to be always inlined.
  * Improved several internal functions that call the automaton.

20230913; version 4.031:
  * Updated ucfdata2.h and updata3.h to support Unicode 15.1.0.
  * Updated updataout3.cpp so that the "Unknown" value can be used as a
    value for Script/Script_Extensions of Unicode property escapes.
    Although this value is mentioned in Scripts.txt, SRELL did not
    support it because it was not included in the table in the
    ECMAScript specification which shows what script names must be
    supported. However, as the table was removed from the specification
    and the rationale to exclude it has disappeared, SRELL has begun to
    support this value, following V8.

20230909; version 4.030:
  * Modified the pattern compiler not to create a rewinder only for ^,
    $, or \b/\B.
  * Introduced the binary search to look up names and values for Unicode
    properties.
  * In accordance with the change above, updated unicode/updataout2.cpp
    to updataout3.cpp.
    Furthermore, since the ECMAScript specification ceased to list the
    script names that must be supported, modified to read them from
    Scripts.txt and PropertyValueAliases.txt.
  * Changed the suffix of Unicode data files from *.hpp to *.h.
  * Updated unicode/ucfdataout2.cpp to follow the suffix change above.

20230903; version 4.029:
  * Updated unicode/updataout2.cpp to fix an issue that caused
    compilation error because internal integer types were unified in
    version 4.023.
  * Recreated srell_updata2.hpp (Data for the two scripts that were
    newly added to Unicode 15 were missing from the previous version.
    Apparently, it was output by the previous version of
    updataout2.cpp).

20230831; version 4.028:
  * Improved not to call the automaton for Unicode code point values
    that cannot be held by a single char/wchar_t when the regex or
    wregex type is used.

20230821; version 4.027:
  * Fixed a bug that caused the first capturing group to be empty in the
    match result of /(?:(\d+-)?)+(\d{1,2})-(\d{1,2})/ against
    "2023-8-21" (This bug had been existing from an early version).
  * Fixed a bug that caused the entire match to be only "23-8-21" in the
    same match result (This bug was introduced in 4.019 and was not
    covered by the fix in 4.026).

20230820; version 4.026:
  * Fix a bug that caused a search for /(\d+-)?\d{1,2}-\d{1,2}/ in
    "2023-8-20" matched only "23-8-20" since version 4.019.

20230819; version 4.025:
  * To avoid movzx, changed the type to hold a flag in the internal
    representation from bool to an integer type.
  * Repleaced names of member variables in structs that are used
    frequently in the automaton with shorter names.

20230817; version 4.024:
  * Commented out the code for an optimisation that had become unused
    since 4.019.
  * Various minor improvements and fixes.

20230804; version 4.023:
  * Unified two internal integer types to one type.
  * Simplified several optimisations that had become less effective
    because of the entry state selector introduced in 4.019.
  * Improved the entry state selector.
  * Corrected misnamed variable names.

20230730; version 4.022:
  * Refinement of source code and various minor fixes.

20230727; version 4.021:
  * Improved the branch optimisation so that SRELL can optimise
    Alternatives without inserting new additional internal states.

20230724; version 4.020:
  * Simplified the method of converting properties of strings to the
    internal representation.
  * Other minor improvements.

* [4.000-4.019, v flag mode] Because there was a mistake in the setting
  for compiling my own source files to a release version, the v flag
  mode was not correctly implemented in SRELL 4.000-4.019. Adding the
  following line at the last of the optimise_pos() function fixes the
  problem:
    insert_btbranch(piece, ins_bt);
  The bug originated from the fact that this function was not called
  from anywhere.

20230114; version 4.019:
  * Implemented a new entry state selector.

20230109; version 4.018:
  * Cancelled the mergence of automata that was done in version 4.016,
    because once I began to modify the pattern compiler for i-modifier
    support, icase search performance degradation that had not surface
    in preliminary examinations appeared.

20230107; version 4.017:
  * Fixed a bug that caused compilation to fail since version 4.006 when
    bidirectional iterators were passed to an algorithm function.

20230106; version 4.016/3.018 (@ only):
  * Merged four automata into two (preparation for i-modifier support).
  @ Fixed the pattern compiler not to treat /a{0,0}/ as an error.
  @ Other minor fixes.

20221227; version 4.015:
  * Fixed a minor issue in regex_iterator2 that was treated as an error
    by VC when _ITERATOR_DEBUG_LEVEL >= 1.
  * Other improvements.

20221220; version 4.014:
  * Supplemented some member functions that were missing accidentally
    from match_results in the previous release.
  * Simplified regex_token_iterator.

20221220; version 4.013:
  * Fixed a minor issue in split(). When splitting "abc" by /$/, split()
    had returned {"abc", ""} instead of {"abc"} that is correct.
  * Reduced the number of overload functions of replace(). Now when the
    lambda expression is used, the type of match_results that will be
    passed to a callback function needs specifying explicitly as the
    template argument.
  * Added regex_iterator2.

20221216; version 4.012:
  * Fixed replace(). VC2005 could not compile it.

20221214; version 4.011/3.017 (@ only):
  @ [LWG Issue 3204] Added swap() to sub_match.
  * Modified replace() so that it can replace any container type that
    looks like std::basic_string.
  * Added srell::str_clip.
  * Added overload functions to split() that support a pair of iterators
    and a pointer.

20221212; version 4.010:
  * Adjusted the behaviour of split() in accordance with the document.
    While the document says sub_match is pushed to a list container,
    in the code basic_string was pushed to the list container.
  * Added overloads to the sub_match class that support implicit and
    explcit converting to std::basic_string instantiated with a custom
    traits/allocator.

20221210; version 4.009/3.016 (@ only):
  @ Fixed a problem so that regex_iterator.prefix().matched can be set
    to true in incrementing after it matched an empty sequence.
  @ Fixed the core of algorithm functions not to cause compilation error
    when an object of match_results instantiated with a custom allocator
    is provided.
  * Added new member functions to basic_regex as API extensions.

20221130; version 4.008:
  * Priority was given back to the BMH matcher from the finder
    introduced in 4.006.
  * Minor improvements of ^ and $ in the multiline mode and \b, \B.

20221124; version 4.007:
  * Added support for the un-bounded flag modifiers ((?ims-ims)), which
    are available only at the beginning of a regular expression (the
    same as Python 3.11).
    Note: This feature is not defined in the ECMAScript specification
    nor compatible with the regexp-modifiers proposal. This feature can
    be disabled by defining SRELL_NO_UBMOD.

20221123; version 4.006:
  * Added a new finder for expressions whose first matching character is
    a single character.

20221030; version 4.005/3.015 (@ only):
  @ Fixed a problem that caused undefined behaviour in conditions where
    sizeof (int) != sizeof (long), e.g. LP64 (4/8/8). (Thanks to Travers
    Ching for the report).
  * Updated unicode/ucfdataout2.cpp and updataout2.cpp. Now they can
    compile even without srell_ucfdata2.hpp and srell_updata2.hpp.
  * Some clean-ups.

20221022; version 4.004/3.014:
  * Updated srell_ucfdata2.hpp and srell_updata2.hpp to support Unicode
    15.0.0.
  * Updated unicode/updataout2.cpp to support Unicode 15. (Support in
    advance new script names that are expected to be available in RegExp
    of ECMAScript 2023).
  * Removed some code that had become unused or meaningless as a result
    of the previous backreference bug fixes.

20221012; version 4.003/3.013:
  * Re-refixed the backreference bug. Incidentally, this bug was
    introduced along with the addition of the variable-length lookbehind
    feature. Therefore, SRELL versions 2.000- have this bug.
    (It originated from the fact that in a variable length lookbehind
    assertion, it is possible that the parser encounters a backreference
    prior to the corresponding bracket pair, such as /(?<=\1\s+(\d+))/,
    and the parser cannot know immediately whether the corresponding
    capturing bracket pair really exists in the expression).

20221012; version 4.002/3.012:
  * Refixed the backreference bug in a different way because the fix of
    20221011 did not cover the problem caused by such an expression as
    /(?:\1+)*()/. Fixed also an infinite loop caused by an expression
    like /()(?:\1+)*/.

20221011; version 4.001/3.011 (@ only):
  @ Fixed a bug that caused dereferencing a null pointer or infinite
    loop when a backreference is followed by * or +, and the
    backreference appears prior to the close bracket of the
    corresponding pair of capturing brackets, such as /\1*()/, /(\1+)/.
    (Thanks to @datadiode, the author of srellcom, for finding the bug).
  * In accordance with the ECMAScript specification, restricted
    positions where '-' can be written without escaping in character
    classes. Now '-' following a predefined character class such as \d,
    \s causes an error, unless it is the final character in a character
    class. ([\s-0] causes an error, [\s-] is accepted).
  * Adjusted internal UTF-8 iterators.

20220618; version 4.000:
  * Added support for the v-flag mode that is expected to be added to
    a future version of ECMAScript.
  * Changed the format of srell_updata.hpp and renamed to
    srell_updata2.hpp.
  * In accordance with the change above, unicode/updataout.cpp was
    updated and renamed to updataout2.cpp.
  * Fixed an issue of a struct layout that clang-tidy warns as
    "excessive padding" on 64-bit systems (Thanks for the report).
  * Updated unicode/ucfdataout2.cpp.

20220529; version 3.010:
  * Reduced the amount of memory used to hold a character class that
    contains Unicode property escapes.
  * Changed the value of error_type thrown when an invalid name or value
    is specified in curly brackets of \p or \P, from
    regex_constants::error_escape to newly-introduced
    regex_constants::error_property.
  * Other minor improvements.

20220511; version 3.009:
  * Fixed an optimisation bug that caused /abcd|ab/ not to match "abc".

20220504; version 3.008:
  * Fixed the behaviour of [^\P{...}] when the icase flag is set, as it
    behaved similarly to the one in v-mode that has been proposed in
    TC39.

20220429; version 3.007:
  * Further modification to the counter mechanism.

20220428; version 3.006:
  * Modified the mechanism of the counter used for repetition.
  * Re-removed the implementation of linear search for small character
    classes.

20220424; version 3.005:
  * Fixed a bug that caused /(?<=$.*)/ not to match the end of "a" when
    the multiline flag is set
  * Preparations for \A, \z, (?m:) that have been proposed in TC39.

20220420; version 3.004:
  * Added a new optimisation for /A*B/ and /A+B/ where a character class
    A overlaps a character or character class B, such as /[A-Za-z]+ing/,
    /".*"/.

20220416; version 3.003:
  * Combined two optimisation functions into one.
  * Reduced the amount of code for lookaround (lookahead and lookbehind)
    assertions.

20220416; version 3.002:
  * Fixed a bug that caused regex_match or regex_search with the
    match_continuous flag being set to fail when the entry state
    selector introduced in version 3.000 was used internally.

20211025; version 3.001:
  * Removed the code for splitting counter as it seemed to be no effect
    or to make performance a bit worse.
  * Fixed potential bugs.
  * Minor improvements.

20211023; version 3.000:
  * Updated srell_ucfdata2.hpp and srell_updata.hpp to support Unicode
    14.0.0.
  * Updated unicode/updataout.cpp to support Unicode 14. (Support in
    advance new script names that are expected to be available in RegExp
    of ECMAScript 2022).
  * Changed the type used to store a Unicode value when char32_t is not
    available, from an "unsigned integer type with width of at least 21
    bits" to a "one of at least 32 bits".
  * Changed the type used to store a repetition count or character class
    number when char32_t is not available, from "unsigned int" to
    "unsigned integer type of at least 32-bit width".
  * Added overflow check in the function that translates digits into a
    numeric value. For example, while up to the previous version
    /a{0,4294967297}/ was treated as /a{0,1}/ because of overflow when
    the unsigned int type is 32-bit width, SRELL now throws error_brace
    in cases like this.
  * Fixed a bug that caused /[^;]*^;?/ not to match the beginning of an
    input string when the multiline flag is not set.
  * Implemented a very simple and limited entry state selector.

20211004; version 2.930:
  * Added new typedefs whose prefix is u1632w- and support UTF-16 or
    UTF-32 depending on the value of WCHAR_MAX. (When 0xFFFF <=
    WCHAR_MAX < 0x10FFFF, u1632w- types are aliases of u16w- types.
    When 0x10FFFF <= WCHAR_MAX, u1632w- types are aliases of u32w-
    types).
  * Reduced the amount of memory used for Eytzinger layout search.
  * Various improvements. (Some of them are based on suggestions to NIRE
    by Marko Njezic).

20210624; version 2.920:
  * Added a new optimisation for the quantifier '?' (I.e., {0,1}).
  * Changed the version number of the ECMAScript specification
    referenced in misc/sample01.cpp to 2021.

20210429; version 2.912:
  * Fixed another bug in the optimisation introduced in version 2.900,
    which caused /aa|a|aa/ not to match "a" (Thanks to Jan Schrötter for
    the report).
    Incidentally, this optimisation can be disabled by defining
    SRELLDBG_NO_BRANCH_OPT2 prior to including srell.hpp.

20210424; version 2.911:
  * Fixed a bug in the optimisation introduced in version 2.900, which
    caused /abc|ab|ac/ not to match "ac". (Thanks for the bug report [As
    my email to the reporter was rejected by the email server and
    returned, it is unclear whether mentioning the name here is okay
    with the reporter. So, I refrain]).

20210407; version 2.910:
  * Fixed a potential memory leak in move assignment operators used by
    the pattern compiler since 2.900. (Thanks to Michal Švec for the
    report).

20210214; version 2.901:
  * Removed redundant template specialisations.

20210214; version 2.900:
  * Added a new optimisation for the alternative expression that consist
    of string literals, such as /abc|abd|acde/.
  * Fixed the problem that brought u(8|16)[cs]regex_(token_)?iterator
    (i.e., regex (token) iterators specialised for char8_t or char16_t)
    to a compile error.
  * Minor improvements.

20210131; version 2.810:
  * Improved internal UTF-8 iterators.

20200724; version 2.800:
  * Introduced the Eytzinger layout for binary search in the character
    class.
  * Reimplemented linear search for small character classes.
  * Modified handling of the property data used for parsing the name for
    a named capturing group. Now they are loaded only when needed
    instead of being loaded into an instance of basic_regex always.

20200714; version 2.730:
  * Added code to prevent redundant save and restore operations when
    nested capturing round brackets are processed.
  * Improved regex_iterator.

20200703; version 2.720:
  * Improved case-insensitive (icase) search using the
    Boyer-Moore-Horspool algorithm for UTF-8 string that includes
    non-ASCII characters or UTF-16 string that includes non-BMP
    characters.
  * Fixed a bug that caused regex_iterator->prefix().first to point to
    the beginning of the subject string instead of the end of the
    previous match (regression introduced in version 2.650, when
    three-iterators overloads were added to regex_search()).
  * In accordance with the fix above, when a three-iterators version of
    regex_search() is called, now match_results.position() returns a
    distance from the position passed to as the lookbehind limit (3rd
    param of regex_search) and match_results.prefix().first points to
    the position passed to as the beginning of the subject string (1st
    param of regex_search).
  * Fixed a bug that could cause a valid UTF-8 sequence being adjacent
    to an invalid UTF-8 sequence to be skipped when the BMH algorithm
    was used (regression introduced in version 2.630, when UTF-8
    handling was modified).

20200701; version 2.710:
  * Minor modifications to Boyer-Moore-Horspool search.

20200630; version 2.700:
  * Optimisation adjustments.

20200620; version 2.651:
  * Move the group name validity check to after parsing the \u escape.
  * Updated misc/sample01.cpp to version 1.103. Changed the version
    number of the ECMAScript specification referenced by to 2020 (ES11).

20200618; version 2.650:
  * To element access functions in match_results, added overload
    functions for specifying the group name by a pointer.
  * When a three-iterators version of regex_search() is used, SRELL now
    sets match_results::prefix::first to the position passed to as the
    lookbehind limit (third param) instead of the position passed to as
    the beginning of the subject (first param).
  * Removed some operations that seem to be redundant.

20200601; version 2.643:
  * Added "inline" to operators in syntax_option_type and
    match_flag_type types, based on a report that it is needed not to
    cause the multiple definition error.
  * Minor improvements.

20200530; version 2.642:
  * Reduced the size of memory allocated by the basic_regex instance.

20200528; version 2.641:
  * The fix in 2.640 was incomplete. Fixed the optimisation bug 1 again.
  * Optimisation adjustments.

20200516; version 2.640:
  * Fixed an optimisation bug 1: It was possible for regex_match to pass
    the end of a subject string under certain conditions.
  * Fixed an optimisation bug 2: ^ and $ were not given a chance to
    match an appropriate position in some cases when the multiline flag
    is set to true.
  * Updated srell_ucfdata2.hpp and srell_updata.hpp.

20200509; version 2.630:
  * SRELL's pattern compiler no longer permits invalid UTF-8 sequences
    in regular expressions. It throws regex_utf8. (Invalid UTF-8
    sequences in the subject string are not treated as an error.)
  * Fixed BMH search functions not to include extra (invalid) UTF-8
    trailing bytes following the real matched substring, in a returned
    result.
  * Fixed minor issues: 1) basic_regex.flags() did not return the
    correct value in some cases, 2) match_results.format() did not
    replace $<NAME> with an empty string when any capturing group whose
    name is NAME did not exist.

20200502; version 2.620:
  * Removed methods used for match_continuous and regex_match in the
    class for the Boyer-Moore-Horspool algorithm. Now SRELL always uses
    the automaton like earlier versions when they are processed.
  * Some clean-ups.

20200428; version 2.611:
  * Fixed a bug that caused /\d*/ not to match the head of "abc" but to
    match the end of it. (regression introduced in version 2.210.)

20200426; version 2.610:
  * Fixed a bug that caused case-insensitive (icase) BMH search to skip
    a matched sequence at the beginning of the entire text, when 1)
    search is done against UTF-8 or UTF-16 text, and 2) the searched
    pattern ends with a character that consists of multiple code units
    in that encoding.
  * Now SRELL parses a capturing group name according to the ECMA
    specification and strictly checks its validity. Group names like
    /(?<,>...)/ cause regex_error.

20200418; version 2.600:
  * To pass to regex_search() directly the limit of a sequence until
    where the automaton can lookbehind, added three-iterators versions
    of regex_search().
  * [Breaking Change] Removed the match_lblim_avail flag from
    match_flag_type and the lookbehind_limit member from match_results
    which were added in version 2.300.
  * Updated srell_ucfdata2.hpp and srell_updata.hpp to support Unicode
    13.0.0.
  * Updated unicode/updataout.cpp to support Unicode 13. (Support in
    advance new script names that will be available in RegExp of
    ECMAScript 2020).

20191118; version 2.500:
  * Modified basic_regex to hold precomputed tables for icase matching,
    instead of creating them from case folding data when its instance is
    first created.
  * In accordance with the change above, srell_ucfdata.hpp and
    ucfdataout.cpp were replaced with srell_ucfdata2.hpp and
    ucfdataout2.cpp, accordingly.
  * Changed the method of character class matching from linear search to
    binary search.
  * Changed the timing of optimisation of a character class from "when a
    closing bracket ']' is found" to "every time a character or
    character range is pushed to its character class array".
  * Removed all asserts.
  * Modified the pattern compiler to interpret sequential \uHHHH escapes
    as a Unicode code point value if they represent a valid surrogate
    pair. (By this change, incompatibilities with the ECMAScript
    specification disappeared.)
  * Fixed the position of an endif directive that caused a compiler
    error when -DSRELL_NO_NAMEDCAPTURE is specified.
  * Updated updataout.cpp to version 1.101.
  * Added a standalone version of SRELL in the single-header directory.

20190914; version 2.401:
  * Reduced the size of basic_regex. (It was bloated by my carelessness
    when support for Unicode property escapes was added).
  * Improved basic_regex::swap().

20190907; version 2.400:
  * Improved the performance of character class matching.
  * Modified the pattern compiler to interpret the \u escape sequence in
    the group name in accordance with the ECMAScript specification.
  * Updated ucfdataout.cpp to version 1.200. A new member has been added
    to the unicode_casefolding class in srell_ucfdata.hpp that
    ucfdataout.cpp generates.
    Because SRELL 2.400 and later need this added member, they cannot be
    used with srell_ucfdata.hpp output by ucfdataout.cpp version 1.101
    or earlier. (No problem in using an older version of SRELL with a
    newer version of srell_ucfdata.hpp).
  * Some clean-ups and improvements.

20190902; version 2.304:
  * Fixed regex_iterator that had been broken by the code clean-up in
    version 2.303.

20190810; version 2.303:
  * Refixed the problem that was fixed in version 2.302 as the fix was
    incomplete.
  * Cleaned up code.

20190809; version 2.302:
  * Bug fix: When (?...) has a quantifier, strings captured by round
    brackets inside it were not cleared in each repetition but carried
    over to the next loop. For example,
    /(?:(ab)|(cd))+/.exec("abcd") returned ["abcd", "ab", "cd"], instead
    of ["abcd", undefined, "cd"]. (The latter is correct).
  * Updated misc/sample01.cpp to version 1.102. Rewrote the chapter
    numbers in accordance with ECMAScript 2019 (ES10).

20190724; version 2.301:
  * In accordance with the ECMAScript spec, restricted the characters
    which can be escaped by '\', to the following fifteen characters:
    ^$\.*+?()[]{}|/
    Only in the character class, i.e., inside [], '-' also becomes a
    member of the group.

20190717; version 2.300:
  * Added a feature for specifying the limit until where the automaton
    can lookbehind, separated from the beginning of a target sequence.
    (Addition of the match_lblim_avail flag to match_flag_type and the
    lookbehind_limit member to match_results).
    And, lookbehind_limit of match_results being private and used
    internally in regex_iterator is also set in its constructor.
  * Removed order restriction of capturing parentheses and
    backreferences, in accordance with the ECMAScript spec. Now /\1(.)/,
    /(?<=(.)\1)/, and /\k<a>(?<a>.)/ are all okay.
  * Updated misc/sample01.cpp to version 1.101. Added one compliance
    test from misc.js.

20190714; version 2.230:
  * Improved the performance of searching when regular expressions begin
    with a character or character class followed by a '*' or '+'. (E.g.
    /[A-Za-z]+ing/).

20190707; version 2.221:
  * Changed the feature test macro used for checking availability of
    std::u8string, from __cpp_char8_t to __cpp_lib_char8_t.
  * When icase specified, if all characters in a character class become
    the same character as a result of case-folding, the pattern compiler
    has been changed to convert the character class to the character
    literal (e.g. /r[Ss\u017F]t/i -> /rst/i).
  * Fixed a minor issue.

20190617; version 2.220:
  * Changed the internal representation of repetition in the case that
    it becomes more compact by not using the counter.
  * Fixed an optimisation bug that caused searching for /a{1,2}?b/
    against "aab" to return "ab" instead of "aab". (Condition: a
    character or character class with a non-greedy quantifier is
    followed by its exclusive character or character class).

20190613; version 2.210:
  * Improved a method of matching for expressions like /ab|cd|ef/ (where
    string literals separaterd by '|' begin with a character exclusive
    to each other).

20190603; version 2.202:
  * Fixed a bug that caused regex_match to behave like regex_search in
    the situation where the BMH algorithm is used.

20190531; version 2.200:
  * For searching with a ordinary (non-regex) string, added an
    implementation based on the Boyer-Moore-Horspool algorithm.
  * Improved UTF-8 iterators.
  * Fixed behaviours of \b and \B when icase specified, to match /.\B./i
    against "s\u017F".
  * Fixed minor issues.

20190508; version 2.100:
  * Fixed a bug that caused failure of capturing when 1) a pair of
    capturing brackets exists in a lookbehind assertion, and 2) variable
    length expressions exist in both the left side of and the inside of
    the pair of brackets. E.g. given "1053" =~ /(?<=(\d+)(\d+))$/, no
    appropriate string was set for $2.
  * Updated srell_ucfdata.hpp and srell_updata.hpp to support Unicode
    12.1.0.
  * Updated unicode/updataout.cpp to support Unicode 12. (Support in
    advance a new binary property and new script names that will be
    available in RegExp of ECMAScript 2019 and new script names that are
    anticipated to be available in RegExp of ECMAScript 2020).
  * Changed the newline character in srell.hpp from CR+LF to LF.
  * Modified unicode/*.cpp to output LF as a newline instead of CR+LF.
  * Updated misc/sample01.cpp to version 1.100:
    1. Rewrote the chapter numbers in subtitles of compliance tests, in
       accordance with ECMAScript 2018 Language Specification (ES9).
       (The old chapter numbers were based on ECMAScript specifications
       up to version 5.1).
    2. Added one compliance test from ECMAScript 2018 Language
       Specification 21.2.2.3, NOTE.
  * Modified the macros for detecting C++11 features.
  * Changed the method of the character class.
  * For all the constructors and assign functions of basic_regex to have
    a default argument for flag_type, reimplemented syntax_option_type
    and match_flag_type (missed changes between TR1 -> C++11).
  * Experimental support for the char8_t type. If a compiler supports
    char8_t (detected by the __cpp_char8_t macro), classes whose names
    have the "u8-" prefix accept a sequence of char8_t and handle it as
    a UTF-8 string. If char8_t is not supported, the classes handle a
    sequence of char as a UTF-8 string, as before.
  * As classes that always handle a sequence of char as a UTF-8 string,
    new classes whose names have the "u8c-" prefix were added. They
    correspond to the classes having the "u8-" prefix in their names up
    to version 2.002:
    * u8cregex; u8ccmatch, u8csmatch; u8ccsub_match, u8cssub_match;
      u8ccregex_iterator, u8csregex_iterator; u8ccregex_token_iterator,
      u8csregex_token_iterator.

20180717; version 2.002:
  * Changed the maximum number of hexdigits in \u{h...} from six to
    'unlimited' in accordance with the ECMAScript specification. ("one
    to six hexadecimal digits" of the old implementation was based on
    the proposal document).
  * Updated updataout.cpp to version 1.001. Encounting unknown
    (newly-encoded) script names is no longer treated as an error.
  * Updated srell_ucfdata.hpp and srell_updata.hpp to support Unicode
    11.0.0.

20180204; version 2.001:
  * When icase is specified, [\W] (a character class containing \W) no
    longer matches any of [KkSs\u017F\u212A] (ecma262 issue #512).

20180127; version 2.000:
  * Added the following features that are to be included into RegExp of
    ECMAScript 2018:
    * New syntax option flag for '.' to match every code point, dotall,
      was added to srell::regex_constants as a value of
      syntax_option_type and to srell::basic_regex as a value of
      flag_type.
    * New expressions to support the Unicode property, \p{...} and
      \P{...}.
    * Named capture groups (?<NAME>...) and the new expression for
      backreference to a named capture group, \k<NAME>.
  * The behaviors of lookbehind assertions changed. Now both (?<=...)
    and (?<!...) support variable-length lookbehind.

20180125; version 1.401:
  * Limited the maximum of numbers that are recognised as backreference
    in match_results.format() up to 99, in accordance with the
    ECMAScript specification. (I.e., restricted to $1..$9 and $01..$99).
  * Removed an unused macro and its related code.

20180101; version 1.400:
  * Changed the behaviour of the pattern compiler so that an empty
    non-capturing group can have a quantifier, for example, /(?:)*/. It
    is a meaningless expression, but changed just for compatibility with
    RegExp of ECMAScript.
  * Fixed a hang bug: This occured when 1) a non-capturing group has a
    quantifier, 2) and the length of the group itself can be zero-width,
    3) and a backreference that can be zero-width is included in the
    group somewhere other than the last, such as /(.*)(?:\1.*)*/.

20171216; version 1.300:
  * Fixed an important bug: /^(;[^;]*)*$/ did not match ";;;;" because
    of a bug in optimisation. This problem occured when a sequence of
    regular expressions ended like /(A...B*)*$/ where a character or
    character set that A represents and the one that B represents are
    exclusive to each other.

20170621; version 1.200:
  * Updated srell_ucfdata.hpp to support Unicode 10.0.0.
  * Improved u8regex_traits to handle corrupt UTF-8 sequences more
    safely.

20150618; version 1.141:
    Updated srell_ucfdata.hpp to support Unicode 8.0.0.

20150517; version 1.140:
  * Modified the method for regex_match() to determine whether a
    sequence of regular expressions is matched against a sequence of
    characters. (Issue raised at #2273 in C++ Standard Library Issues
    List).
  * Restricted the accepted range of X in the expression "\cX" to
    [A-Za-z] in accordance with the ECMAScript specification.
  * Fixed the problem that caused parens in a lookaround assertion not
    to capture a sequence correctly in some circumstances because the
    bug fix done in version 1.111 was imperfect.

20150503; version 1.130:
  * Improved case-folding functions.
  * Updated unicode/ucfdataout.cpp to version 1.100.
  * Fixed a typo in #if directives for u(16|32)[cs]match.

20150425; version 1.120:
  * Fixed the bug that caused characters in U+010000-U+10FFFF in UTF-8
    (i.e., four octet length characters) not to have been recognised.
  * Updated misc/sample01.cpp to version 1.010.

20150402; version 1.111:
  * Fixed the problem that caused $2 of "aaa" =~ /((.*)*)/ to be empty
    instead of "aaa" because of a bug in optimisation.

20141101; version 1.110:
  * Several fixes based on a bug report:
      1. Added "this->" to compile() in basic_regex::assign().
      2. Implemented operator=() functions explicitly instead of using
         default ones generated automatically.
  * unicode/ucfdataout.cpp revised and updated to version 1.001.

20140622; version 1.101:
    Updated srell_ucfdata.hpp to support Unicode 7.0.0.

20121118; version 1.100:
    The first released version.

